I was just talking to another mom. My son has gone through a depression since lock down. He's a teenager though. She has a younger child about the age of yours that said is experiencing these same kinds of changes. They are working to normalize things. But yes, a diagnosis of diabetes and not having it treated prior can certainly impact a child. Hope all is well. Best wishes to your son. Diabetic educators are so helpful guiding families.
One question would be, other than corona, did anything happen that might have triggered something in him? Maybe he saw something, or heard something, or experienced something. Getting him to talk about it would be the most helpful thing, and if you're not the person he's going to talk to there are pediatric psychologists who specialize in doing that.